Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicament, such as liquid drugs, and further providing administration of the medicament to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose. In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
Typically, the medicament to be administered is provided in a cartridge that has a moveable piston or bung mechanically interacting with a piston rod of a drive mechanism of the drug delivery device. By applying thrust to the piston in a distal direction, a predefined amount of the medicinal fluid is expelled from the cartridge.
Especially with disposable drug delivery devices and pen-type injectors, the various components and parts the drug delivery device is made of typically comprise injection moulded plastic components. Also the housing of such drug delivery devices comprises various housing components of thermoplastic material. Most typically, drug delivery devices of pen-injector type typically comprise a distal housing component that serves as a cartridge holder and further comprise a proximal housing component to engage with the distal housing component and being further adapted to accommodate a drive mechanism to operably engage with the cartridge for dispensing a predefined amount of the medicament provided therein.
When the housing components are manufactured as injection moulded plastic parts, which, by virtue of appropriately selected thermoplastic materials feature a particular elasticity, such components can support a snap-fitting and an inseparable positively engaged interconnection.
However, since such drug delivery devices are predominately intended for home medication, the device has to fulfil highest possible standards in terms of failure safety and robustness, especially in view of mechanical impact.
Moreover, the mutual interconnection of the distal and proximal housing components has to be rather rigid and free of tolerances in order to immediately provide a counter force when a dose dispensing action is initiated, during which the drive mechanism of the drug delivery device exerts distally directed thrust or pressure towards the piston of the cartridge.
If for instance such a device drops down from a considerably height, a mechanical load-distribution may rise above a critical level in the interconnection of cartridge holder and body. Such point stresses or point loading may well exceed a critical level and as a consequence the interconnection of cartridge holder and body may break down such that device would be no longer of use.
One possible object of the present invention is to provide a mechanically stable, reliable, cost-efficient and precisely fitting housing for a drug delivery device in particular for a pen-type injector.